For a spark-ignition internal combustion engine, it is customary for fuel to be injected by way of an injector constructed as an assembly of component parts, with the assembly fitted to the engine as a unit. The injector is then connected to fuel and electrical power supplies. Where fuel is delivered by the injector into a combustion chamber entrained in a gas such as air (such as, for example, by way of the arrangement disclosed in the Applicant's U.S. Pat. No. 4,693,224, the contents of which are included herein by reference), the injector is also typically connected to an air supply such as a gas compressor. Typically, the injector in such a dual fluid injection system is adapted to be coupled to the various supplies through a fuel and air supply rail (such as, for example, as is disclosed in the Applicant's U.S. Pat. No. RE 36768, the contents of which are also included herein by reference) arranged to deliver services to all of the injectors fitted to the engine. The injector is provided with appropriate connectors for connection to the fuel and air supply rail. The injector is also provided with one or more electrical terminals for connection to electrical control circuitry as necessary.
Typically, the injector has a delivery end section with a delivery port through which fuel is injected into the combustion chamber. The delivery end section generally includes a valve seat, and a valve member movable into and out of sealing engagement with the valve seat for selectively opening and closing the delivery port. The valve member forms part of a valve having a valve stem, one end of which supports the valve member. An electromagnetic system is typically utilised for operation of the valve to selectively open and close the delivery port. The electromagnetic system includes a solenoid coil located in the body of the injector about the valve stem, and a solenoid armature attached to the valve stem. Energisation of the solenoid coil typically induces movement of the armature to cause the valve member to move out of engagement with the valve seat against the influence of a spring which normally retains the valve in the sealing or closed condition.
In a dual fluid fuel system, because the injector needs to be coupled to the air and fuel supply rail and also to the electrical control circuitry, it is necessary to ensure that the connectors and the electrical terminals on the injector are correctly aligned in relation to counterpart components with which they are to mate when the injector is in the installed condition. This requires careful installation of the injector in the engine.
It is also necessary to calibrate the valve with respect to the electromagnetic means so that the stroke length of the valve induced by energisation of the electromagnetic means is properly related to the extent to which the valve is required to open. Because of the manner in which the valve is constructed and assembled, typically, calibration of the valve can only be performed after it has been fully assembled. This can often present some difficulties in terms of the accuracy, stability and reliability of calibration.
The difficulties referred to above are likely to increase significantly in circumstances where the fuel injector is combined in a single unit with an ignition means. In such circumstances, it is also necessary to provide a high tension current path for ignition purposes, and there are also associated insulation considerations. This generally requires that the injector be constructed from various materials, some having electrically conductive properties and others having electrically insulating properties. It is the presence of these various materials that often creates significant difficulties in relation to calibration.
Examples of arrangements involving combined fuel injection and ignition means are disclosed in U.S. Pat. No. 4,967,708 (Linder et al), EP 0 632 198 (Suzuki), U.S. Pat. No. 5,497,744 (Nagaosa et al), and U.S. Pat. No. 5,730,100 (Bergsten). Each of the combined fuel injection and ignition means disclosed therein are one-piece assemblies which can be cumbersome to install and maintain and which generally have alignment difficulties as discussed above when in the installed condition. Furthermore, such arrangements typically involve complicated connections for high voltage current paths which exist therein, and so are fraught with safety problems.
It is against this background, and the problems and difficulties associated therewith, that the present invention has been developed.